Inductive winding



Feb. 9, 1943. o. T. FARRY INDUCTIVE W INDING Filed May 31, 1940 FIGS.

INVENTOR TIS T.FARRY BY ATTORNEY Patented Feb. 9, 1943 INDUCTIVE WINDING Otis T. Fan-y, University City, Mo., assignor to Wagner Electric Corporation, St. Louis, Mo., a

corporation 01' Delaware Application May 31, 1940, Serial No. 338,015

3 Claims.

In alternating current inductive apparatus, such as choke coils, transformers and the like, it is often necessary to employ a conductor having large cross sectional area in order to carry the desired current without undue heating. If a single conductor is used heavy eddy currents are set up in the conductor with resultant losses. For this, as well as mechanical reasons ithas been customary to employ a composite winding composed of a member of insulated smaller conductors or strands connected in parallel.

If such strands are of ribbon or flat form wound concentrically the outer strand will be of greatest length and the inner strand of least length, the other strands being of intermediate lengths. Due to the difference of lengths of the strands the total current will not be divided evenly among them as they have difierent resistances. This fault is augmented by the fact that the self-inductance caused by leakage flux is diiferent in the various strands. To overcome this difllculty it is common practice to make use of what is known as transposition to even the length of the strands of the conductors. This transposition has usually been accomplished by twisting the composite winding through an angle of 180 at the central point of its length.

The object of my invention is to provide an improved form of winding in which transposition is secured by transferring individual strands of the conductor from one side to the other thereof at uniform intervals in its length. By this means the transposition requires the minimum amount of space, mechanical construction of the coil is made easy and insulation at the points of transfer of the strand is facilitated.

In the accompanying drawing which illustrates one form of winding made in accordance with my invention, Figure 1 is a semi-diagrammatic view of a transformer including such winding; Figure 2 is a bottom plan view, on an enlarged scale, of a portion of one turn of the winding at the point of transposition of a strand; Figure 3 is a section taken on the line 3--3 of Figure 2 showing six turns of the winding; Figure 4 is a section taken on the line 44 of Figure 2. showing a simgle turn of the winding; Figure 5 is a view showing the first step in bending a strand for a transposition, and Figure 6 is a view showing the second step of such bending.

Referring first to Figures 1 and 3, the transformer comprises a core I and, a winding 2. The latter is composed of six strands indicated by the letters a to f. The number of turns in the winding should be equal to the number of strands in the conductor employed or some multiple thereof. In the drawing I have shown a transformer in which the winding has eighteen turns. The transposition of a strand, therefore, takes place at every third turn so that the winding consists of six groups of three turns each indicated by the letters A to F. In each group the strands are in the same sequence. In group A the sequence of the strands counting from the outside to the inside is a, b, c, d, e, f. In group B the sequence is b, c, d, e, I, a. The remaining groups have similar receding sequences, strand 0 forming the outer layer of the coils of group C, strand d the outer layer of those of group D, etc.

The transposition of a strand may be accomplished without severing it by bending it in the manner shown in Figures 5 and 6. Where the transposition is to be made a strand, as for example a, is bent in its own plane to form two parallel branches, 3 and 4 with an inclined connecting portion 5. The extent of this bend is such thatthe distance h between dotted lines 1 and 8 (Figure 5) denoting extensions of the adjacent ewes of branches 3 and 4, is equal to the thickness of five strands plus sufficient space for insulation. The two branches are now bent at right angles to the connecting portion 5 as shown in Figure 6. In this position the branches will again be parallel but will lie in planes separated by the distance h. The selected strand may now be positioned to straddle the remaining five strands as shown in Figure 2. Where this transposition or cross-over occurs it is desirable to insulate the connection 5 to prevent short circuiting the remaining strands. This may be readily accomplished by means of a U-shaped sheet of insulating material 9 applied as shown. It will be understood that where the transposition takes place the composite winding will be off-set a distance equal to the thickness of one strand so that the diameter of the coil is not varied by such transposition.

It will be evident that this type of transposition results in strands of the same length as such strand occupies in rotation each position in the sequence of strands; and further that it assumes each position through the same number of turns. Moreover but little more copper is required than in a similar coil without transposition and no appreciable increase in space is required. This is due to the fact that the strand in its passage from one side to the other of the winding lies flat against the edge of the helix. The method of securing the transposition is readily adaptable to the usual manufacturing operation as the copper strips are wound simultaneously from reels. It is only necessary to interrupt such winding operation at the points of transfer long enough to perform the simple bending operation strand, said transposition taking place at substantially uniform intervals in the length of the winding and changing the position of only one strand at each point of transposition, said transposition being secured by an integral loop formed in the strand by twisting it through an angle of 180, said loop being positioned astride the untransposed strands with the same side of the transposed strand toward the inner and outer peripheries of said untransposed strands.

2. An inductive winding for electrical apparatus comprising a plurality of coils formed of strands wide relative to their thickness, said strands being wound concentrically face-to-face one upon another, said strands being transposed to secure uniform total length of each strand, said transposition taking place at substantially uniform interval in the length of the winding and changing the position of only one strand at each point of transposition, said transposition being secured by an integral loop formed in the strand by twisting through an angle of said loop being positioned astride the untransposed strands with the same wide face presented toward the inner and outer peripheries and the edges of said untransposed strands.

3. The method of transposing one strand of a composite coil inductive winding from one side to the other of the coil, said coil consisting of rectangular strands wound concentrically one upon another, which consist in bending the strand in its own plane to orm two parallel branches and a connecting portion, bending the branches at right angles to the connecting portion to form a loop, and placing the loop astride the remaining strands of the coil'to complete the transposition.

OTIS T. FARRY. 

